Heretofore, an inner liner layer which contains a butyl-based rubber exhibiting suppressed permeation of gases such as butyl rubber and a halogenated butyl rubber as the main component is disposed at the inner face of a pneumatic tire so that leak of the air is prevented and the internal pressure of the tire is kept constant. However, when the content of the butyl-based rubber is increased, strength of the rubber in the unvulcanized condition is decreased, and fracture and formation of holes tend to take place in rubber sheets. In particular, when the thickness of the inner liner is decreased, a problem arises in that the cord at the inner face of a tire tend to be exposed at the surface during production of the tire.
Therefore, the amount of the butyl-based rubber which can be used is naturally limited. When a rubber composition containing the butyl-based rubber described above is used, the inner liner layer is required to have a thickness of about 1 mm from the standpoint of the air barrier property. Due to this restriction, the weight of the inner liner layer occupies as great as about 5% of the weight of the entire tire. This causes a problem when the weight of the tire is decreased to improve the fuel economy of an automobile.
In response to the recent social requirement for saving energy, methods for decreasing the thickness of the inner liner layer are proposed so that the weight of an automobile can be decreased. For example, a method in which a nylon film layer or a vinylidene chloride layer is used as the inner liner layer in place of the conventional butyl-based rubber layer, is disclosed (for example, refer to Patent References 1 and 2). A method in which a film of a composition comprising a blend of a thermoplastic resin such as a polyamide-based resin and a polyester-based resin with an elastomer is used as the inner liner layer, is disclosed (for example, refer to Patent Reference 3).
However, although the weight of the tire can be decreased to some degree, the above methods have problems in that crack resistance and bending fatigue resistance are inferior to those of conventional layers of compositions containing butyl-based rubber, in particular, when the inner liner layer is used at a low temperature of 5° C. or lower since the matrix material is a crystallizable resin material, and that the process for producing the tire is complicated.
On the other hand, it is known that an ethylene-vinyl alcohol copolymer (hereinafter, referred to as EVOH, occasionally) exhibits an excellent gas barrier property. Since the air permeability of EVOH is one hundredths or smaller of the rubber composition for the inner liner comprising butyl-based rubber, the property for maintaining the internal pressure can be remarkably improved even when the thickness is 50 μm or smaller, and the decrease in the weight of the tire can also be achieved. Therefore, it is expected that the use of EVOH for the inner liner is effective for decreasing the air permeability of the pneumatic tire. For example, a pneumatic tire having an inner liner comprising EVOH is disclosed (for example, refer to Patent Reference 4).
However, when EVOH is used for the inner liner, fracture or formation of cracks takes place occasionally under deformation by bending since the modulus is much greater than that of rubber conventionally used for tires although a great effect of improving the property of maintaining the internal pressure is exhibited. Therefore, a problem arises in the use of the inner liner comprising EVOH in that, although the property for maintaining the internal pressure is remarkably improved before the tire is used, the tire after being used, which has been subjected to bending deformations due to rotation of the tire during the use, exhibits a decreased property for maintaining the internal pressure than that exhibited before being used.
To overcome the above problem, for example, an inner liner for use at the inner face of a tire, which comprises a resin composition comprising 60 to 99% by weight of an ethylene-vinyl alcohol copolymer having a content of 20 to 70% by mole of ethylene and a degree of saponification of 85% or greater and 1 to 40% by weight of a hydrophobic plasticizer, is disclosed (for example, refer to Patent Reference 5). However, the bending resistance is not always sufficiently satisfactory.
Therefore, development of an inner liner which exhibits a great bending resistance and enables to achieve a decrease in the thickness while the sufficient gas barrier property is maintained has been desired.
As the above inner liner, for example, a laminate obtained by integrally adhering a film or a sheet of a rubbery elastomer exhibiting excellent bending resistance and a film of a thermoplastic resin exhibiting excellent gas barrier property may be considered. It is required for this laminate that an excellent average peel strength between the layer of a rubbery elastomer and the layer of a film of a thermoplastic resin be exhibited.    [Patent Reference 1] Japanese Patent Application Laid-Open No. Heisei 7 (1995)-40702    [Patent Reference 2] Japanese Patent Application Laid-Open No. Heisei 7 (1995)-81306    [Patent Reference 3] Japanese Patent Application Laid-Open No. Heisei 10 (1998)-26407    [Patent Reference 4] Japanese Patent Application Laid-Open No. Heisei 6 (1994)-40207    [Patent Reference 5] Japanese Patent Application Laid-Open No. 2002-52904